Accept him whose faith is weak, without passing judgment on disputable matters. One man's faith allows him to eat everything, but another man, whose faith is weak, eats only vegetables. The man who eats everything must not look down on him who does not, and the man who does not eat everything must not condemn the man who does, for God has accepted him. Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand. One man considers one day more sacred than another; another man considers every day alike. Each one should be fully convinced in his own mind. He who regards one day as special, does so to the Lord. He who eats meat, eats to the Lord, for he gives thanks to God; and he who abstains, does so to the Lord and gives thanks to God. For none of us lives to himself alone and none of us dies to himself alone. If we live, we live to the Lord; and if we die, we die to the Lord. So, whether we live or die, we belong to the Lord.
The issue of gray areas and Christian liberty can be difficult waters to navigate. Being able to properly discern a gray area presupposes that you already know what the Bible expressly forbids. This is only complicated by the fact that God laid down some rules for for the Israelites in the Old Testament that no longer apply to Christians today. How are we to handle all of this?
A simple attitude of grace and humility is needed, as well as honesty between you and the Lord about your own "areas of conscience", those things that others may do but you cannot. As the passage above points out, both parties on either side of an area of conscience can fall prey to a judgmental attitude. Those who partake in a gray matter (ha ha, brain joke) may be tempted to look down on those who do not as being weaker Christians. And those who do not partake in a gray matter may be tempted to condemn as sinful those who do.
No matter which side of such issues you fall on, the guideline is to treat your fellow believers with sensitivity and grace. The freedom we have in Christ is not freedom to sin (liscence) but rather freedom to fellowship with both stronger and weaker Christians in an attitude of humility, rather than dividing down lines of conscience.
However, this should not be confused with the idea that we should never judge, confront, or hold accountable a fellow follower of Christ. When an issue crosses over from a gray area into something that is prohibited in black and white terms by the Bible (for instance drinking a beer crosses over into many beers and getting drunk), it ceases to be a gray area and becomes a matter that must be dealt with in the manner Jesus laid out for us in Matthew 18.